Squib circuit low side battery short protection

ABSTRACT

A squib driver circuit for deployment of an active safety restraint in a vehicle. The squib driver circuit may include a low side protection circuit. The low side protection circuit may include a comparator circuit to compare a voltage at a low side return terminal to a reference voltage and activate a timer in response to the voltage at the low side return terminal exceeding the reference voltage, the timer generating a disable signal to disable the low side driver after a predetermined period of time. The low side protection circuit may disable the low side driver after the short is detected and elapse of the predetermined period of time. The squib driver circuit may be formed on a single chip.

BACKGROUND

The present application relates generally to a voltage regulatorintegrated into a squib driver circuit.

An airbag system typically includes a restraint control module, areaction canister, an air bag, and an inflator with ignitor (squib) thatare stored inside the reaction canister. The inflator with squib isconnected to the restraint control module via conductive wires andconnectors. The total electrical path of these wires and connectors toand from the inflator is termed “squib loop”. The restraint controlmodule provides sufficient energy to the inflator through the squib loopto provide airbag actuation. The inflator is actuated by the restraintcontrol module once appropriate signals are received from vehiclesensors are sufficient to warrant airbag activation. The restraintcontrol module controls the overall operation of the air bag system andcan be viewed as the main control unit for the air bag system.

As with any electrical system that consists of sensors, airbag, wiringand connectors etc, the system requires electrical connections tooperate properly. Specifically, in airbag safety systems is determinedby customer demand that diagnostic capability be implemented in therestraint control module to interrogate the squib loop for proper squibloop resistance value as well as other characteristics that may preventthe air bag from being activated improperly.

BRIEF SUMMARY

A method and system for protecting the squib loop drivers in a restraintcontrol module is disclosed in the present application. The deploymentfunction of the restraint control module is provided by the activationof the squib loop drivers to send the all-fire current for the specifiedall-fire time through the ignitor. The squib loop drivers are comprisedof both a high-side and a low-side squib driver. The squib driverprotection concept is to attempt the deployment function until a systemfault occurs. If a system fault occurs then the deployment function willbe terminated in order to protect the squib loop drivers. System faultsmay include short circuit to Ground, shorted squib load, short circuitto Vbat (e.g. vehicle battery voltage), faulted energy reserve supply,and others.

Further objects, features and advantages of this application will becomereadily apparent to persons skilled in the art after a review of thefollowing description, with reference to the drawings and claims thatare appended to and form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings the components are not necessarily toscale, emphasis instead being placed upon illustrating the principles ofthe application. Moreover, like reference numerals designatecorresponding parts throughout the views.

FIG. 1 is a schematic illustration of a squib driver circuit.

FIG. 2 is a schematic illustration of a short to ground fault for thesquib driver circuit of FIG. 1.

FIG. 3 is a schematic illustration of a short to ground fault for thesquib driver circuit of FIG. 1.

FIG. 4 is a schematic illustration of a shorted squib load fault for thesquib driver circuit of FIG. 1.

FIG. 5 is a schematic illustration of short to battery fault for thesquib driver circuit of FIG. 1.

FIG. 6 is a schematic illustration of short to battery fault for thesquib driver circuit of FIG. 1.

FIG. 7 is a schematic illustration of a faulty external transistor forthe squib driver circuit of FIG. 1.

FIG. 8 is a schematic illustration of another implementation of a squibdriver circuit.

FIG. 9 is a schematic illustration of a short to ground fault for thesquib driver circuit of FIG. 8.

FIG. 10 is a schematic illustration of a short to ground fault for thesquib driver circuit of FIG. 8.

FIG. 11 is a schematic illustration of a shorted squib load fault forthe squib driver circuit of FIG. 8.

FIG. 12 is a schematic illustration of short to battery fault for thesquib driver circuit of FIG. 8.

FIG. 13 is a schematic illustration of short to battery fault for thesquib driver circuit of FIG. 8.

FIG. 14 is a schematic illustration of a faulty external transistor forthe squib driver circuit of FIG. 8.

DETAILED DESCRIPTION

Airbag safety restraint systems typically employ a single inflatordevice to produce inflation gas for inflating a vehicle occupantrestraint airbag the event of a collision. The inflator device iscontrolled by a squib driver circuit. The squib driver circuit mayinclude a high side driver and as low side driver implemented on asingle deployment chip.

FIG. 1 is a schematic illustration of a squib driver circuit 100. Thesquib driver circuit includes a deployment chip 110. The deployment chip110 may be a single silicon chip, for example, an ASIC (ApplicationSpecific Integrated Circuit). The deployment chip 110 may include aninput terminal (SS_(xy)) 142 for receiving an input voltage. The inputvoltage may be used to fire a deployable restraint such as an air bag.The input terminal (SS_(xy)) 142 may receive the input voltage from abattery such as vehicle battery 105. A switch 116 such as the powertransistor may be located between the input terminal (SS_(xy)) 142 andthe battery 105. The battery 105 may be connected to the switch 116through a diode, further the switch may be connected to an electricalground though a diode and capacitor (C_(ER)) 108.

The switch 116 may control power provided to the input terminal 142 fromthe battery 105 as directed by an enable switch 114. The enable switch114 may receive enable voltage 138 from an output terminal (VSF) 140 ofthe deployment chip 110. The output voltage may be provided from theoutput terminal 140 (VSF) to the enable switch 114. The microprocessorcontrol circuit 112 may control the enable switch 114. When the enableswitch 114 is active, the enable voltage may be provided to activateswitch 116 allowing the battery 105 to provide power to the inputterminal (SS_(xy)) 142. In some implementations, the enable switch 114may be connected to the gate of a power transistor thereby acting as aswitch or regulator allowing the battery 105 to provide power to theinput terminal (SS_(xy)) 142. In some implementations, the switch 116may be an N-channel MOSFET with a drain in connection with the battery105 and a source in connection with the input terminal (SS_(xy)) 142. Inthis implementation, a resistor may be placed between the gate andsource to allow proper operation. The switch 116 can be a MOSFET thatprovides two functions: Firstly, switch 116 can provide a redundantsilicon control path that can prevent deployment in case of systemfailure where, for example Switch 116 is disabled and switches 124 and134 of deployment chip 110 become active due to a common failure mode.Secondly, switch 116 can provide a reduced and more controlledV(SS_(xy),0) 142 when implemented as a pass element part of a closedloop regulator control path and hence absorb more power and provide alower level of power dissipation on the expensive ASIC squib drivertransistors to minimize system cost.

The input terminal (SS_(xy)) 142 may be connected to a high side drivercircuit 121. The high side driver circuit 121 may be connected betweenthe input terminal 142 and the high side feed terminal 144. In oneimplementation, a power transistor 124 may be connected between theinput terminal (SS_(xy)) 142 and the high side feed terminal (SF_(x))144. The power transistor 124 may be an N-channel MOSFET with a drainconnected to the input terminal (SS_(xy)) 142 and a source connected tothe high side feed terminal (SF_(x)) 144. A gate of the power transistor124 may be connected to a high side gate driver circuit 122. In someimplementations, a current sensor 126 may provide a current signal tothe high side gate driver circuit 122. The gate driver circuit 122 mayutilize the current signal to control activation of the power transistor124 in response to the amount of current flow. The current sensor 126may be located between the power transistor 124 and the high side feedterminal (SF_(x)) 144. The high side feed terminal (SF_(x)) 144 may beconnected to an ignitor (R_ignitor) 118 through a feed wire(R_Wire_Feed) 147. The current may be returned from the ignitor 118through a return wire (R_Wire_Return) 148 to a low side return terminal(SR_(x)) 146.

A low side driver circuit 131 may be connected between the low sidereturn terminal 146 and an electrical ground. In one implementation, apower transistor 134 may be connected between the return terminal(SR_(x)) 146 and the electrical ground. The power transistor 134 may bean N-channel MOSFET with a drain connected to the return terminal(SR_(x)) 146 and a source connected to the electrical ground. A gate ofthe power transistor 134 may be connected to a low side gate drivercircuit 132. In some implementations, a current sensor 136 may provide acurrent signal to the low side gate driver circuit 132. The gate drivercircuit 132 may utilize the current signal to control activation of thepower transistor 134 in response to the amount of current flow. Thecurrent sensor 136 may be located between the power transistor 134 andthe electrical ground.

A digital control circuit 120 may receive commands from a communicationinterface 130, such as a serial communication interface. The commandsprovided to the digital circuit 120 through the communication interface130 may include an enable command, an all fire command, as well asvarious configuration commands to set timer durations or thresholds forvarious components such as the high side gate driver 122 or the low sidegate driver 132.

The wire, connectors, clock-springs, EMI inductors and squib may all becomprised of linear conductive components and can be combined orsimplified into an equivalent resistance of R_Wire_Feed (resistance ofthe feed wire 147) and R_Wire_Return (resistance of the return wire148). The pyrotechnic device with the ignitor is represented byR_Ignitor (resistance of the ignitor circuit 118). AssumingR_Wire_Feed=0 Ohm, R_Wire_Return=0 Ohm, The effects on the high sidedriver (HSD) and the low side driver (LSD) can be estimated. Consideringno fault conditions as shown in FIG. 1, the energy absorbed by the HSD(E_HSD) and the energy absorbed by the LSD (E_LSD) isE_HSD=[(V(SS_(xy),0)−I_All-Fire*(R_ignitor+Rdson_LSD)*I_All-Fire]*[T_All-Fire]E_LSD=[I_All-Fire{circumflex over ( )}2*(Rdson_LSD)]*T_All-Fire

Where V(SS_(xy),0) [142] is the voltage between pin SS_(xy) and ground(e.g. 33 V), I_All-Fire is the current required to fire the deployabledevices (e.g. 1.75 A, 1.2 A), Rdson_LSD is the resistance of the lowside driver (e.g. 1 Ohm, resistance across transistor 134), T_All-Fireis the amount required to fire all of the deployable devices (e.g. 500μseconds, 2000 μseconds).

One fault condition may include a short of the SF_(x) (high side feedterminal 144) to ground. A simulated illustration of this fault isprovided by the ground 190 in FIG. 2. Considering the system whendriving a faulted condition of SF_(x) pin short circuit to ground andimpact to the HSD, the energy absorbed by the HSD and LSD isE_HSD=[(V(SS_(xy),0))*I_All-Fire]*T_All-FireE_LSD=0 joules

One fault condition may include a short of the SR_(x) pin (low sidereturn terminal 146) to ground. A simulated illustration of this faultis provided by the ground 191 in FIG. 3. Considering the system drivinga faulted condition of SR_(x) pin short circuit to ground and impact tothe HSD, the energy absorbed by the HSD and LSD isE_HSD=[(V(SS_(xy),0)−(I_All-Fire*R_Ignitor))*I_All-Fire]*T_All-FireE_LSD=0 joules

Another fault condition may include a short of the SF_(x) pin (high sidefeed terminal 144) to the SR_(x) pin (low side return terminal 146). Asimulated illustration of this fault is provided by the shunt 192 inFIG. 4. Considering the system when driving a faulted condition ofSF_(x) pin short to SR_(x) pin (shorted squib load) and impact to theHSD, the energy absorbed by the HSD and LSD isE_HSD=[(V(SS_(xy),0)−I_All-Fire*(Rdson_LSD))*I_All-Fire]*T_All-FireE_LSD=[I_All-Fire{circumflex over ( )}2*(Rdson_LSD)]*T_All-Fire

Another fault condition may include a short of the SR_(x) pin (low sidereturn terminal 146) to battery voltage. A simulated illustration ofthis fault is provided by the battery 193 in FIG. 5. Considering thesystem when driving a faulted condition of SR_(x) pin short to Vbat andimpact to the LSD, the energy absorbed by the HSD and LSD isE_HSD=[(V(SS_(xy),0)−(I_All-Fire*R_Ignitor)−Vbat)*I_All-Fire]*T_All-FireE_LSD=[I_LSD*Vbat]*T_All-Fire

Another fault condition may include a short of the SF_(x) pin (high sidefeed terminal 144) to battery voltage. A simulated illustration of thisfault is provided by the battery 194 in FIG. 6. Considering the systemwhen driving a faulted condition of SF_(x) pin short to Vbat and impactto the LSD, the energy absorbed by the HSD and LSD isE_HSD=[(V(SS_(xy),0)−Vbat)*I_All-Fire]*T_All-FireE_LSD=[(Vbat−(I_LSD*R_Ignitor))*I_LSD]*T_All-Fire

Another fault condition may include a faulty external transistor. Asimulated illustration of this fault is provided by the shunt 195 inFIG. 7. Considering the system when driving a faulted condition ofexternal transistor and impact to the HSD, the energy absorbed by theHSD and LSD isE_HSD=[(V_(ER))−I_All-Fire*(R_Ignitor+Rdson_LSD))*I_All-Fire]*T_All-FireE_LSD=[I_All-Fire{circumflex over ( )}2*(Rdson_LSD)]*T_All-Fire

Where V_(ER) is the voltage at node 107 (e.g. 33V)

FIG. 8 is a schematic illustration of another squib driver circuit 200.The squib driver circuit includes a deployment chip 210. The deploymentchip 210 may be a single silicon chip, for example, an ASIC (ApplicationSpecific Integrated Circuit). The deployment chip 210 may include aninput terminal 242 for receiving an input voltage. The input voltage maybe used to fire a deployable restraint such as an air bag. The inputterminal 242 may receive the input voltage from a battery such asvehicle battery 205. A switch 216 such as the power transistor may belocated between the input terminal 242 and the battery 205.

The switch 216 may control power provided to the input terminal 242 fromthe battery as directed by an enable switch 214. The enable switch 214may receive enable voltage from an output terminal 240 of the deploymentchip 210. The output voltage may be provided from the output terminal240 to the enable switch 214. The microprocessor control circuit 212 maycontrol the enable switch 214. When the enable switch 214 is active, theenable voltage may be provided to activate switch 216 allowing thebattery to provide power to the input terminal 242. In someimplementations, the enable switch 214 may be connected to the gate of apower transistor thereby acting as a switch or regulator allowing thebattery 205 to provide power to the input terminal 242. In someimplementations, the switch 216 may be an N-channel MOSFET with a drainin connection with the battery 205 and a source in connection with theinput terminal 242. In this implementation, a resistor may be placedbetween the gate and source to allow proper operation. The switch 216can be a MOSFET that provides two functions: Firstly, switch 216 canprovide a redundant silicon control path that can prevent deployment incase of system failure where, for example switch 216 is disabled andswitches 221 and 231 of deployment chip 210 become active due to acommon failure mode. Secondly, switch 216 can provide a reduced and morecontrolled V(SS_(xy),0) 242 when implemented as a pass element part of aclosed loop regulator control path and hence absorb more power andprovide a lower level of power dissipation on the expensive ASIC squibdriver transistors to minimize system cost.

The input terminal 242 may be connected to a high side driver circuit221. The high side driver circuit 221 may be connected between the inputterminal 242 and the high side feed terminal 244. In one implementation,a power transistor 224 may be connected between the input terminal 242and the high side feed terminal 244. The power transistor 224 may be anN-channel MOSFET with a drain connected to the input terminal 242 and asource connected to the high side feed terminal 244. A gate of the powertransistor 224 may be connected to a high side gate driver circuit 222.In some implementations, a current sensor 226 may provide a currentsignal to the high side gate driver circuit 222. The gate driver circuit222 may utilize the current signal to control activation of the powertransistor 224 in response to the amount of current flow. The currentsensor 226 may be located between the power transistor 224 and the highside feed terminal 244. The high side feed terminal 244 may be connectedto an ignitor 218 through a feed wire having a resistance 247. Thecurrent may be returned from the ignitor 218 through a return wirehaving a resistance 248, to a low side return terminal 246.

A low side driver circuit 231 may be connected between the low sidereturn terminal 246 and an electrical ground. In one implementation, apower transistor 234 may be connected between the return terminal 246and the electrical ground. The power transistor 234 may be an N-channelMOSFET with a drain connected to the return terminal 246 and a sourceconnected to the electrical ground. A gate of the power transistor 234may be connected to a low side gate driver circuit 232. In someimplementations, a current sensor 236 may provide a current signal tothe low side gate driver circuit 232. The gate driver circuit 232 mayutilize the current signal to control activation of the power transistor234 in response to the amount of current flow. The current sensor 236may be located between the power transistor 234 and the electricalground.

A digital control circuit 220 may receive commands from a communicationinterface 230, such as a serial communication interface. The commandsprovided to the digital circuit 220 through the communication interface230 may include an enable command, an all fire command, as well asvarious configuration commands to set timer durations or thresholds forvarious components such as the high side gate driver 222 or the low sidegate driver 232.

A voltage regulator 282 may be provided between output terminal 240 andinput terminal 242. The voltage regulator includes an amplifier 280,with a voltage divider connected to one input of the amplifier 280, andthe other input connected to an electrical ground. The output of theamplifier 280 is connected to the output terminal 240.

The role of the voltage regulator 282 can be two-fold. First, thevoltage regulator 282 may provide a reduced level of voltage to thesquib driver SS_(xy) pin (input terminal 242) to provide the deploymentfunction. This also reduces the absorbed energy of the squib driverswhile providing the deployment function into the normally expectedconditions, as well as, during some fault conditions. The second role ofthe regulator may be to provide less variation in the expected value ofthe squib driver SS_(xy) pin (input terminal 242) to again reduceabsorbed energy of the squib drivers. As such, the voltage regulator 282may keep the voltage at the input terminal 242 at the minimum levelneeded for firing the safety device. In some implementations the minimumvoltage level may be 10-20V volts depending on the firing current andloop resistance.

A high side short to battery & Faulty SS_(xy) protection circuit 284 mayinclude a comparator 250. The comparator 250 may be configured tocompare at the voltage input terminal 242 to a reference voltage 252. Insome implementations, the voltage at the input terminal 242 may bescaled using a voltage divider 251. As such, the comparator 250 maydetermine if the voltage at the input terminal 242 exceeds the referencevoltage 252 and generate a voltage limit signal that indicates thevoltage at the terminal 242 has exceeded the reference voltage 252. Inaddition, the high side gate driver circuit 222 may generate a currentlimit signal indicating that the current through the power transistor224 has exceeded a current threshold. Further, the high side gate drivercircuit 222 may generate an active signal indicating that high side gatedriver has been activated, for example, by the digital control circuit220. An AND circuit 254 may receive the voltage limit signal, thecurrent limit signal, and the active signal. The AND circuit 254 maygenerate a condition signal that is provided to a delay timer 256. TheAND circuit 254 may generate the condition signal based on one of or acombination of the active signal, the current limit signal, and thevoltage limit signal. For example, the AND circuit 254 may generate thecondition signal based on the current limit signal and the voltage limitsignal, or the voltage limit and the active signal. In one particularimplementation, the AND circuit may generate a condition signal inresponse to all of the active signal, current limit signal, and voltagelimit signal being present. (e.g. simultaneously)

In some implementations, the deployment chip 210 may include atemperature sensor measuring the temperature of the high side transistor224. An over temperature signal may be provided from the temperaturesensor to the AND circuit 254. The AND circuit 254 may generate thecondition signal based on one of or a combination of an over temperaturesignal, the active signal, the current limit signal, and the voltagelimit signal. For example, the AND circuit 254 may generate thecondition signal based on the current limit signal and the overtemperature signal, or the voltage limit and the over temperaturesignal. In one particular implementation, the AND circuit 254 maygenerate a condition signal in response to all of the over temperaturesignal, active signal, current limit signal, and voltage limit signalbeing present. (e.g. simultaneously)

The delay timer 256 may start timing based on the condition signal beingactive. The delay timer 256 may help in situations where petaling of thecanister may cause shorting, for example, to the inflator housing duringnormal deployment. The delay timer 256 count may reset once the countingcondition is no longer met, (e.g. if one of the active signal, currentlimit signal, and voltage limit signal are not present). Alternativelyin some implementations, the delay timer may accumulate across multipleperiods where the triggering signals (active signal, current limitsignal, and/or voltage limit signal) are present. The delay time countedby the delay timer 256 may be a fractional part of the deployment time(e.g. may be less than 1/10 th of the deployment time) As such in someimplementations, the amount of time that the delay timer 256 counts maybe less than 120 microseconds. The amount of time that the delay timer256 counts may be set through by the digital control circuit 220, forexample based on commands received over the communication interface 230.Once the delay timer has counted for a predetermined amount of time, thedelay timer 256 may generate a disable signal to be provided to an ORcircuit 258. If the OR circuit 258 receives the disable signal from thedelay timer 256, the OR circuit 258 may generate a disable signal thatis then provided to the high side gate circuit 222 to disable the powertransistor 224.

The role of the high side short to battery & Faulty SS_(xy) protectioncircuit 284 can be to allow the squib drivers to attempt deployment witha higher than expected or allowed SS_(xy) pin voltage, due to either aHSD short to Vbat or a faulted SS_(xy) regulation system (e.g. a faultin voltage regulator 282), for a definable period of time after which adetected fault will terminate deployment and keep the squib drivers frombeing destroyed or damaged.

A high side short to ground protection circuit 286 may include acomparator 260. The comparator 260 may be configured to compare thevoltage at the high side feed terminal 244 to a reference voltage 262.As such, the comparator 260 may determine if the voltage at the highside feed terminal 244 is below a reference voltage and generate avoltage limit signal that indicates the voltage at the terminal 244 isless than the reference voltage. In addition, the high side gate drivercircuit 222 may generate a current limit signal indicating that thecurrent through the power transistor 224 has exceeded a currentthreshold. Further, the high side gate driver circuit 222 may generatean active signal indicating that high side gate driver has beenactivated, for example, by the digital control circuit 220. An ANDcircuit 264 may receive the voltage limit signal, the current limitsignal, and the active signal. The AND circuit 264 may generate acondition signal that is provided to a delay timer 266. The AND circuit264 may generate the condition signal based on the one of or acombination of the active signal, the current limit signal, and thevoltage limit signal. For example, the AND circuit 264 may generate thecondition signal based on the current limit signal and the voltage limitsignal, or the voltage limit and the active signal. In one particularimplementation, the AND circuit 264 may generate a condition signal inresponse to all of the active signal, current limit signal, and voltagelimit signal being present. (e.g. simultaneously).

In some implementations, the deployment chip 210 may include atemperature sensor measuring the temperature of the high side transistor224. An over temperature signal may be provided from the temperaturesensor to the AND circuit 264. The AND circuit 264 may generate thecondition signal based on one of or a combination of an over temperaturesignal, the active signal, the current limit signal, and the voltagelimit signal. For example, the AND circuit 264 may generate thecondition signal based on the current limit signal and the overtemperature signal, or the voltage limit and the over temperaturesignal. In one particular implementation, the AND 264 circuit maygenerate a condition signal in response to all of the over temperaturesignal, active signal, current limit signal, and voltage limit signalbeing present. (e.g. simultaneously).

The delay timer 266 may start timing based on the condition signal beingactive. The delay timer 266 may help in situations where petaling of thecanister may cause shorting for example to the inflator housing duringnormal deployment. The delay timer 266 count may reset once the countingcondition is no longer met, (e.g. if one of the active signal, currentlimit signal, and voltage limit signal are not present). Alternatively,in some implementations, the delay timer may accumulate across multipleperiods where the triggering signals (active signal, current limitsignal, and/or voltage limit signal) are present. The delay time countedby the delay timer 266 may be a fractional part of the deployment time(e.g. may be less than 1/10 th of the deployment time) As such, in someimplementations, the amount of time that the delay timer 266 counts maybe less than 120 microseconds. The amount of time that the delay timer266 counts may be set through by the digital control circuit 220, forexample based on commands received over the communication interface 230.Once the delay timer has counted for a predetermined amount of time, thedelay timer 266 may generate a disable signal to be provided to ORcircuit 258. If the OR circuit 258 receives the disable signal from thedelay timer 266, the OR circuit 258 may generate a disable signal thatis then provided to the high side gate circuit 222 to disable the powertransistor 224.

The role of the high side short to ground protection circuit 286 can beto allow the squib drivers to attempt deployment with a lower thanexpected or allowed SF_(x) pin voltage, due to either a HSD SF_(x) shortto ground, for a definable period of time after which a detected faultwill terminate deployment and keep the squib drivers from beingdestroyed or damaged.

A low side short to battery protection circuit 288 may include acomparator 270. The comparator 270 may be configured to compare thevoltage at the low side return terminal 246 to a reference voltage 272.In some implementations, the voltage at the low side return terminal 246may be scaled using a voltage divider 271. As such, the comparator 270may determine if the voltage at the low side return terminal 246 exceedsa reference voltage and generate a voltage limit signal that indicatesthe voltage at the terminal 246 has exceeded the reference voltage. Insome implementations, the reference voltage may be 5 volts or above. Inaddition, the low side gate driver circuit 232 may generate a currentlimit signal indicating that the current through the power transistor234 has exceeded a current threshold. Further, the low side gate drivercircuit 232 may generate an active signal indicating that low side gatedriver has been activated, for example, by the digital control circuit220. An AND circuit 274 may receive the voltage limit signal, thecurrent limit signal, and the active signal. The AND circuit 274 maygenerate a condition signal that is provided to a delay timer 276. TheAND circuit 274 may generate the condition signal based on the one of ora combination of the active signal, the current limit signal, and thevoltage limit signal. For example, the AND circuit 274 may generate thecondition signal based on the current limit signal and the voltage limitsignal, or the voltage limit and the active signal. In one particularimplementation, the AND circuit 274 may generate a condition signal inresponse to all of the active signal, current limit signal, and voltagelimit signal being present. (e.g. simultaneously)

In some implementations, the deployment chip 210 may include atemperature sensor measuring the temperature of the low side transistor234. An over temperature signal may be provided from the temperaturesensor to the AND circuit 274. The AND circuit 274 may generate thecondition signal based on one of or a combination of an over temperaturesignal, the active signal, the current limit signal, and the voltagelimit signal. For example, the AND circuit 274 may generate thecondition signal based on the current limit signal and the overtemperature signal, or the voltage limit and the over temperaturesignal. In one particular implementation, the AND circuit 274 maygenerate a condition signal in response to all of the over temperaturesignal, active signal, current limit signal, and voltage limit signalbeing present. (e.g. simultaneously)

The delay timer 276 may start timing based on the condition signal beingactive. The delay timer 276 count may reset once the counting conditionis no longer met, (e.g. if one of the active signal, current limitsignal, and voltage limit signal are not present). Alternatively, insome implementations, the delay timer may accumulate across multipleperiods where the triggering signals (active signal, current limitsignal, and/or voltage limit signal) are present. The delay time countedby the delay timer 276 may be a fractional part of the deployment time(e.g. may be less than 1/10th of the deployment time) As such, in someimplementations, the amount of time that the delay timer 276 counts maybe less than 120 microseconds. The amount of time that the delay timer276 counts may be set through by the digital control circuit 220, forexample based on commands received over the communication interface 230.Once the delay timer 276 has counted for a predetermined amount of time,the delay timer 276 may generate a disable signal to be provided to thelow side gate circuit 232 to disable the power transistor 234.

The role of the low side short to battery protection circuit 288 can beto allow the squib drivers to attempt deployment with a higher thanexpected or allowed SF_(x) pin voltage, due to either a LSD short toVbat, for a definable period of time after which a detected short willterminate deployment and keep the squib drivers from being destroyed ordamaged.

Considering all of the previous fault modes (Short to Ground, ShortedSquib Load, Short to Battery) the protection circuits illustrated inFIG. 8 provide significant benefits compared to the system illustratedin FIG. 1. The Energy absorbed by the HSD and LSD is the same as thesystem illustrated in FIG. 1 for a non-faulted system.E_HSD=[(V(SS_(xy),0)−I_All-Fire*(R_ignitor+Rdson_LSD)*I_All-Fire]*T_All-FireE_LSD=[I_All-Fire{circumflex over ( )}2*(Rdson_LSD)]*T_All-Fire

One fault condition may include a short of the SF_(x) (high side feedterminal 244) to ground. A simulated illustration of this fault isprovided by the ground 290 in FIG. 9. Considering the system whendriving a faulted condition of SF_(x) pin short circuit to ground andimpact to the HSD, the energy absorbed by the HSD and LSD isE_HSD=[(V(SS_(xy),0)−I_All-Fire*(R_ignitor+Rdson_LSD))*I_All-Fire]*T_Digital_Delay2E_LSD=0 Joules

Where T_Digital_Delay2 is the amount of time that a fault condition isdetected by the timer 266 before the switch controller 222 isdeactivated (e.g. 10-250 μseconds).

This E_HSD result is now reduced from T_All-Fire to T_Digital_Delay2when compared with the system illustrated in FIG. 1.(25E-06/500E-06=1/20 of the energy).

One fault condition may include a short of the SR_(x) pin (low sidereturn terminal 246) to ground. A simulated illustration of this faultis provided by the ground 291 in FIG. 10. Considering the system whendriving a faulted condition of SR_(x) pin short circuit to ground andimpact to the HSD, the energy absorbed by the HSD and LSD isE_HSD=[(V(SS_(xy),0)−I_All-Fire*(R_ignitor+Rdson_LSD))*I_All-Fire]*T_Digital_Delay2E_LSD=0 Joules

This E_HSD result is now reduced from T_All-Fire to T_Digital_Delay2when compared with the system illustrated in FIG. 1.(25E-06/500E-06=1/20 of the energy).

Another fault condition may include a short of the SF_(x) pin (high sidefeed terminal 244) to the SR_(x) pin (low side return terminal 146). Asimulated illustration of this fault is provided by the shunt 292 inFIG. 11. Considering the system when driving a faulted condition ofSF_(x) pin Short to SR_(x) pin (shorted squib load) and impact to theHSD, the Energy absorbed by the HSD and LSD isE_HSD=[(V(SS_(xy),0)−I_All-Fire*(R_Ignitor+Rdson_LSD))*I_All-Fire]*T_Digital_Delay2E_LSD=0 Joules

This E_HSD result is now reduced from T_All-Fire to T_Digital_Delay2when compared to the system illustrated in FIG. 1. (25E-06/500E-06=1/20of the energy).

Another fault condition may include a short of the SR_(x) pin (low sidereturn terminal 246) to battery voltage. A simulated illustration ofthis fault is provided by the battery 293 in FIG. 12. Considering thesystem when driving a faulted condition of SR_(x) pin short circuit toVbat and impact to the LSD, the energy absorbed by the HSD and LSD isE_HSD=[(V(SS_(xy),0)−(I_All-Fire*R_ignitor)−Vbat)*I_All-Fire]*T_Digital_Delay2E_LSD=[I_LSD*Vbat]*T_Digital_Delay3

Where T_Digital_Delay3 is the amount of time that a fault condition isdetected by the timer 276 before the switch controller 232 isdeactivated (e.g. 10-250 μseconds).

The E_HSD result is now reduced from T_All-Fire to T_Digital_Delay3compared to the system illustrated in FIG. 1. (25E-06/500E-06=1/20 ofthe energy). The E_LSD result is now reduced from T_All-Fire toT_Digital_Delay3 compared to the system illustrated in FIG. 1.(25E-06/500E-06=1/20 of the energy)

Another fault condition may include a short of the SF_(x) pin (high sidefeed terminal 244) to battery voltage. A simulated illustration of thisfault is provided by the battery 294 in FIG. 13. Considering the systemwhen driving a faulted condition of SF_(x) pin short circuit to Vbat andimpact to the LSD, the energy absorbed by the HSD and LSD isE_HSD=[(V(SS_(xy),0)−Vbat)*I_All-Fire]*[T_All_Fire]E_LSD=[(Vbat−(I_LSD*R_Ignitor))*I_LSD]*T_Digital_Delay3

The E_HSD result is the same from T_All-Fire to T_All-Fire when comparedwith the system illustrated in FIG. 1. (500E-06/500E-06=1/1 of theenergy). The E_LSD result is now reduced from T_All-Fire toT_Digital_Delay3 compared with the system illustrated in FIG. 1.(25E-06/500E-06=1/20 of the energy).

Another fault condition may include a faulty external transistor. Asimulated illustration of this fault is provided by the shunt 295 inFIG. 14. Considering the system when driving a faulted condition ofexternal transistor and impact to the HSD, the energy absorbed by theHSD and LSD isE_HSD=[((V_(ER))−I_All-Fire*(R_Ignitor+Rdson_LSD)*I_All-Fire]*T_Digital_Delay1E_LSD=[I_All-Fire{circumflex over ( )}2*(Rdson_LSD)]*T_Digital_Delay3

Where V_(ER) is the voltage at node 207 (e.g. 33V) and Digital_Delay1 isthe amount of time that a fault condition is detected by the timer 256before the switch controller 222 is deactivated (e.g. 10-250 μseconds).

The E_HSD result is now reduced from T_All-Fire to T_Digital_Delay1compared to the system illustrated in FIG. 1. (25E-06/500E-06=1/20 ofthe energy). The E_LSD result is now reduced from T_All-Fire toT_Digital_Delay3 compared to the system illustrated in FIG. 1.(25E-06/500E-06=1/20 of the energy).

The methods, devices, processing, and logic described above may beimplemented in many different ways and in many different combinations ofhardware and software. For example, all or parts of the implementationsmay be circuitry that includes an instruction processor, such as aCentral Processing Unit (CPU), microcontroller, or a microprocessor; anApplication Specific Integrated Circuit (ASIC), Programmable LogicDevice (PLD), or Field Programmable Gate Array (FPGA); or circuitry thatincludes discrete logic or other circuit components, including analogcircuit components, digital circuit components or both; or anycombination thereof. The circuitry may include discrete interconnectedhardware components and/or may be combined on a single integratedcircuit die, distributed among multiple integrated circuit dies, orimplemented in a Multiple Chip Module (MCM) of multiple integratedcircuit dies in a common package, as examples.

The circuitry may further include or access instructions for executionby the circuitry. The instructions may be stored in a tangible storagemedium that is other than a transitory signal, such as a flash memory, aRandom Access Memory (RAM), a Read Only Memory (ROM), an ErasableProgrammable Read Only Memory (EPROM); or on a magnetic or optical disc,such as a Compact Disc Read Only Memory (CDROM), Hard Disk Drive (HDD),or other magnetic or optical disk; or in or on another machine-readablemedium. A product, such as a computer program product, may include astorage medium and instructions stored in or on the medium, and theinstructions when executed by the circuitry in a device may cause thedevice to implement any of the processing described above or illustratedin the drawings.

The implementations may be distributed as circuitry among multiplesystem components, such as among multiple processors and memories,optionally including multiple distributed processing systems.Parameters, databases, and other data structures may be separatelystored and managed, may be incorporated into a single memory ordatabase, may be logically and physically organized in many differentways, and may be implemented in many different ways, including as datastructures such as linked lists, hash tables, arrays, records, objects,or implicit storage mechanisms. Programs may be parts (e.g.,subroutines) of a single program, separate programs, distributed acrossseveral memories and processors, or implemented in many different ways,such as in a library, such as a shared library (e.g., a Dynamic LinkLibrary (DLL)). The DLL, for example, may store instructions thatperform any of the processing described above or illustrated in thedrawings, when executed by the circuitry.

As a person skilled in the art will readily appreciate, the abovedescription is meant as an illustration of the principles of thisdisclosure. This description is not intended to limit the scope orapplication of this disclosure in that the systems and methods aresusceptible to modification, variation and change, without departingfrom spirit of this disclosure, as defined in the following claims.

What is claimed is:
 1. A squib driver circuit for deployment of anactive safety restraint in a vehicle, the squib driver circuit being anintegrated circuit formed on a single chip comprising: an input terminalfor receiving an input voltage used to fire the active safety restraint;a high side feed terminal configured for communication with the activesafety restraint; a low side return terminal configured forcommunication with the active safety restraint; a high side driverconfigured to supply current from the input terminal to the high sidefeed terminal; a low side driver configured to supply current from thelow side return terminal to the electrical ground; and a low side shortto battery voltage protection circuit configured to allow an all firesignal from the low side return terminal until a short is detectedbetween the low side return terminal and a battery voltage for apredetermined period of time and disable the low side driver after theshort is detected and elapse of the predetermined period of time,wherein the low side short to battery voltage protection circuitcomprises a comparator circuit to compare a voltage at the low sidereturn terminal to a reference voltage to determine if the low sidereturn terminal is shorted to the battery voltage, and wherein the lowside short to battery voltage protection circuit comprises a currentsensor to determine if a current through the low side return terminal isabove a current limit; and a timer wherein the low side short to batteryvoltage protection circuit receives a low side enable signal, and thetimer is activated to count when all of the low side enable signal isactive and current exceeds the current limit and the voltage at the lowside return terminal exceeds the reference voltage.
 2. The squib drivercircuit according to claim 1, further comprising a timer configured togenerate a low side disable signal when the voltage at the low sidereturn terminal exceeds the reference voltage for the predeterminedperiod of time.
 3. The squib driver circuit according to claim 1,further comprising a timer configured to generate a low side disablesignal when the current exceeds the current limit for the predeterminedperiod of time.
 4. The squib driver circuit according to claim 1,wherein the low side driver comprises a low side driver transistor and agate control circuit.
 5. The squib driver circuit according to claim 4,wherein the current sensor is located between the low side drivertransistor and an electrical ground.
 6. The squib driver circuitaccording to claim 1, further comprising a serial command interface forproviding an all fire signal.
 7. The squib driver circuit according toclaim 1, wherein a serial command interface is configured to receive acommand to adjust the predetermined period of time.
 8. The squib drivercircuit according to claim 1, wherein the predetermined period of timeis a fractional portion of a deployment time of the active safetyrestraint.
 9. A squib driver circuit for deployment of an active safetyrestraint in a vehicle, the vehicle having an electrical ground and abattery with a battery voltage, the squib driver circuit being anintegrated circuit formed on a single chip comprising: an input terminalfor receiving an input voltage used to fire the active safety restraint;a high side driver configured to supply current from the input terminalto the active safety restraint; a low side driver configured to supplycurrent from the active safety restraint to the electrical ground; and alow side protection circuit comprising a comparator circuit to compare avoltage at a low side return terminal to a reference voltage andactivate a timer in response to the voltage at the low side returnterminal exceeding the reference voltage, the timer generating a disablesignal to disable the low side driver after a predetermined period oftime, wherein the low side protection circuit comprises a current sensorto determine if a current through the low side driver is above a currentlimit; and wherein the low side protection circuit receives a low sideenable signal, and the timer is activated to count when all of the lowside enable signal is active and current exceeds the current limit andthe voltage at the low side return terminal exceeds the referencevoltage.
 10. The squib driver circuit according to claim 9, wherein thetimer is configured to generate a low side disable signal when thecurrent exceeds the current limit and the voltage at the low side returnterminal exceeds the reference voltage for the predetermined period oftime.
 11. The squib driver circuit according to claim 9, wherein the lowside driver comprises a low side driver transistor and a gate controlcircuit.
 12. The squib driver circuit according to claim 11, wherein acurrent sensor is located between the low side driver transistor and theelectrical ground.
 13. The squib driver circuit according to claim 9,further comprising a serial command interface for receiving an all firesignal.
 14. The squib driver circuit according to claim 9, furthercomprising a serial command interface configured to receive a command toadjust the predetermined period of time.
 15. A squib driver circuit fordeployment of an active safety restraint in a vehicle, the vehiclehaving an electrical ground and a battery with a battery voltage, thesquib driver circuit being an integrated circuit formed on a single chipcomprising: an input terminal for receiving an input voltage used tofire the active safety restraint; a high side feed terminal incommunication with the active safety restraint; a low side returnterminal in communication with the active safety restraint; a high sidedriver configured to supply current from the input terminal to the highside feed terminal; a low side driver configured to supply current fromthe low side return terminal to the electrical ground; a low side shortto battery voltage protection circuit configured to allow an all firesignal from the low side return terminal until a first short is detectedbetween the low side return terminal and the battery voltage for a firstpredetermined period of time and disable the low side driver after thefirst short is detected and elapse of the first predetermined period oftime; and at least one of: a high side short to battery voltageprotection circuit configured to allow an all fire signal from the highside feed terminal until a second short is detected between the highside feed terminal and the battery voltage for a second predeterminedperiod of time and disable the high side driver after the second shortis detected between and elapse of the second predetermined period oftime; and a high side short to ground protection circuit configured toallow an all fire signal from the high side feed terminal until a thirdshort is detected between the high side feed terminal and the electricalground for a third predetermined period of time and disable the highside driver after the third short is detected and elapse of the thirdpredetermined period of time.